1. Field of the Invention
The field of art to which the claimed invention pertains is solid-bed adsorptive separation. More specifically, the claimed invention relates to a process for the separation of the ortho, meta and para isomers of chloronitrobenzene from a feed mixture comprising those isomers, which process employs solid adsorbent.
2. Description of the Prior Art
The chloronitrobenzenes are important starting material for the manufacture of azo and sulfur dyes and they also find application in the synthesis of fungicides, preservatives, photochemicals, and pharamaceuticals.
Chloronitrobenzenes are prepared commercially by nitrating chlorobenzene. Chlorobenzene is nitrated at 40.degree.-70.degree. C. with mixed acid (52.5% H.sub.2 SO.sub.4, 35.5% HNO.sub.3 and 12% H.sub.2 O). The nitration product is a mixture of 34% o-chloronitrobenzene, 65% p-chloronitrobenzene and 1% m-chloronitrobenzene.
The methods known to the art for separating the chloronitribenzene isomers of the nitration product mixture are complicated and costly. The washed and neutralized reaction mixture must first be cooled to 16.degree. C. and is held at this temperature which is just above the eutectic point of the mixture. Approximately half of the material crystallizes as the pure para isomer and is separated from the mother liquor. The liquid mixture must then be carefully fractionated in efficient columns to separate the isomers. The first fraction is p-chloronitrobenzene with the meta isomer, the second is mainly the para compound and the third, obtained by distillation without the column, is essentially o-chloronitrobenzene. These distillates are finally fractionally crystallized with very small amounts of methanol to separate the essentially ortho and para isomers. The noncrystallizing liquors and methanol solutions are recycled and the meta isomer is obtained by periodic concentration and separation.
Other no less complicated and costly methods known to be used for separating the ortho and para isomers from the mother liquor from the first crystallization are (a) by fractional crystallization in ethanol, (b) by the addition of 1,4-dichlorobenzene, which breaks the eutectic mixture and permits the separation of the isomers, and (c) by removing the o-chloronitrobenzene by the formation of o-nitrodiphenylamine with aniline and an alkali metal carbonate at 200.degree. C.; the unreacted para isomer is purified by distillation.
It is well known in the separation art that certain crystalline aluminosilicates can be used to separate hydrocarbon species from mixtures thereof. The separation of normal paraffins from branched chained paraffins for example can be accomplished by using a type A zeolite which has pore openings from 3 to about 5 Angstroms. Such a separation process is disclosed in U.S. Pat. Nos. 2,985,589 and 3,201,491. These adsorbents allow a separation based on the physical size differences in the molecules by allowing the smaller or normal hydrocarbons to be passed into the cavities within the zeolitic adsorbent, while excluding the larger or branched chain molecules.
U.S. Pat. Nos. 3,265,750 and 3,510,423, for example, disclose processes in which larger pore diameter zeolites such as the type X or type Y structured zeolites can be used to separate olefinic hydrocarbons.
In addition to separating hydrocarbon types, the type X or type Y zeolites have also been employed in processes to separate individual hydrocarbon isomers. In the process described in U.S. Pat. No. 3,114,782, for example, a particular zeolite is used as an adsorbent to separate alkyl-trisubstituted benzene; and in U.S. Pat. No. 3,668,267 a particular zeolite is used to separate specific alkyl-substituted naphthalenes. In processes described in U.S. Pat. Nos. 3,558,732; 3,686,342 and 3,997,620 adsorbents comprising particular zeolites are used to separate para-xylene from feed mixtures comprising para-xylene and at least one other xylene isomer by selectively adsorbing para-xylene over the other xylene isomers. In the last mentioned processes the adsorbents used are para-xylene selectives; para-xylene is selectively adsorbed and recovered as an extract component while the rest of the xylenes and ethylbenzenes are all relatively unadsorbed with respect to para-xylene and are recovered as raffinate components. Also, in the last mentioned processes the adsorption and desorption may be continuously in a simulated moving bed countercurrent flow system, the operating principles and sequence of which are described in U.S. Pat. No. 2,985,589.
I have discovered that the problems and shortcomings of the known methods of separation of chloronitrobenzene isomers as described above can be avoided by the application of principles, involving the use of zeolites to separate individual hydrocarbon isomers, to the separation of chloronitrobenzene isomers. My invention comprises the use of specific zeolites, for separation of the isomers of chloronitrobenzene.